Polyvinyl alcohol having 1,2-glycol bond in side chain and process for preparing the same

ABSTRACT

There is disclosed a polyvinyl alcohol having a 1,2-glycol bond in a side chain, and a process for preparing the polyvinyl alcolnol wherein there is no generation of dimethyl carbonate hence no need of a process of eliminating dimethyl carbonate in the recovering process of waste liquid after hydrolysis. Also, even when an introduction amount of 1,2-glycol bonds is increased, there is no deterioration of solubility in a hydrolyzing solution (methanol) of a copolymer (paste) before hydrolysis. Further, water-insolubility is not lowered even in experiencing thermal history. Specifically, there is provided a polyvinyl alcohol having a 1,2-glycol bond in a side chain obtained by hydrolyzing a copolymer of a vinyl ester monomer and a compound shown in the formula (1) wherein the hydrolysis degree of the polyvinyl alcohol is at least 60% by mol.

RELATED APPLICATION

This application is a U.S. national phase application of internationalapplication no. PCT/JP2004/011834 filed Aug. 18, 2004.

TECHNICAL FIELD

The present invention relates to a polyvinyl alcohol having a 1,2-glycolbond in a side chain and a process for preparing the same.

BACKGROUND ART

Conventionally, polyvinyl alcohol has been widely used in emulsifiers,suspending agents, surfactants, fiber processing agents, various kindsof binders, paper processing agents, adhesives, films and the like byutilizing film forming characteristics (such as film forming property,oil resistance and strength), water solubility and the like. Inaddition, it is generally used as an aqueous solution except for specialcases.

According to intended uses, polyvinyl alcohols with various degrees ofhydrolysis are used, in the case of using a polyvinyl alcohol with arelatively high degree of hydrolysis, when it is dissolved in water toobtain an aqueous solution, a viscosity of the aqueous solutionincreases with time when a water temperature is low such as duringwintertime to result in poor fluidity, and in an extreme case, theaqueous solution gels and loses fluidity completely, which causesserious problems.

To solve these problems, there is proposed a polyvinyl alcohol having a1,2-glycol bond in a side chain obtained by hydrolysis/decarbonating acopolymer of a vinyl ester monomer and vinyl ethylene carbonate (seeJP-A-2002-241433). The polyvinyl alcohol was excellent in high-speedcoating and adhesion performance.

This polyvinyl alcohol is excellent in the above-mentioned variousphysical properties, however, vinyl ethylene carbonate is used tointroduce 1,2-glycol bonds in a high modification amount (e.g. at least7% by mol) in the polyvinyl alcohol, in this case, in hydrolysis ofpolyvinyl acetate to which vinyl ethylene carbonate is introduced and ina process of eliminating unreacted vinyl acetate monomers frompolymerized paste of polyvinyl acetate to which vinyl ethylene carbonateis introduced, solubility of the resin in solvents such as methanoltends to be lowered, thus there was a limitation of the modificationamount in a preparation process such as hydrolysis conducted withordinary solvents industrially generally used. Also, in deriving vinylethylene carbonate into diol by hydrolysis with alkali, there remained aproblem that byproducts such as dimethyl carbonate contaminated in asolvent recovery system must be treated.

DISCLOSURE OF INVENTION

As a result of intensive studies on the above problems, theabove-described problems have been solved by a polyvinyl alcohol havinga 1,2-glycol bond in a side chain obtained by hydrolyzing a copolymer ofa vinyl ester monomer and a compound shown in the following formula (1),further, it was found that water solubility and standing stability ofthe polyvinyl alcohol can be significantly improved, and the presentinvention reached the completion.

(wherein R¹ is a hydrogen atom or an alkyl group, R² is a single bond oran alkylene group having 1 to 3 carbon atoms which may have an alkylgroup, each of R³ and R⁴ are independently a hydrogen atom or R⁵—CO—(wherein R⁵ is an alkyl group)).

Also, the present invention is characterized in that problem that apolyvinyl alcohol with a degree of hydrolysis of less than 99.0% by mol(partially hydrolyzed material) in experiencing thermal history can besolved by using the compound shown in the above described formula (1).

Namely, the present invention relates to a polyvinyl alcohol having a1,2-glycol bond in a side chain obtained by hydrolyzing a copolymer of avinyl ester monomer and a compound shown in the formula (1).

The present invention also relates to a process for preparing apolyvinyl alcohol having a 1,2-glycol bond in a side chain, wherein thecopolymer of a vinyl ester monomer and a compound shown in the formula(1) is hydrolyzed.

It is preferable that the degree of hydrolysis is at least 99.0% by molor less than 99.0% by mol.

It is more preferable that the copolymerization ratio of the compoundshown in the formula (1) is 0.1 to 40% by mol.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a ¹H-NMR chart of the polyvinyl alcohol (I) obtained inExample 1.

FIG. 2 is a ¹H-NMR chart of the polyvinyl alcohol (II) obtained inExample 1.

FIG. 3 is a ¹H-NMR chart of the polyvinyl alcohol (I) obtained inExample 3.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to a polyvinyl alcohol having a 1,2-glycolbond in a side chain.

The polyvinyl alcohol of the present invention is obtained byhydrolyzing a copolymer of a vinyl ester monomer and a compound shown inthe following formula (1),

(wherein, R¹ is a hydrogen atom or an alkyl group, preferably a methylgroup, an ethyl group or a butyl group, R² is a single bond or analkylene group having 1 to 3 carbon atoms which may have an alkyl group,preferably a methyl group, an ethyl group or a butyl group, each of R³and R⁴ are independently a hydrogen atom or R⁵—CO— (wherein R⁵ is analkyl group, preferably a methyl group, a propyl group, a butyl group, ahexyl group or an octyl group)).

Examples of the compound shown in the formula (1) are3,4-dihydroxy-1-butene, 3,4-diacyloxy-1-butene,3-acyloxy-4-hydroxy-1-butene, 4-acyloxy-3-hydroxy-1-butene,3,4-diacyloxy-2-methyl-1-butene, 4,5-dihydroxy-1-pentene,4,5-diacyloxy-1-pentene, 4,5-dihydroxy-3-methyl-1-petene,4,5-diacyloxy-3-methyl-1-petene, 5,6-dihydroxy-1-hexene and5,6-diacyloxy-1-hexene. Among these, 3,4-diacyloxy-1-butene ispreferable from the viewpoints that it is excellent in copolymerizationreactivity and industrial handling, and among 3,4-diacyloxy-1-butene,3,4-diacetoxy-1-butene is more preferable.

Additionally, 3,4-diacyloxy-1-butene can be commercially available fromEastman Chemical Co., Ltd. and Acros Inc.

Examples of the vinyl ester monomer are vinyl formate, vinyl acetate,vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate,vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinylbenzoate, and vinyl versatate. Of these, vinyl acetate is preferablyused from the viewpoint of economy.

Also, in the present invention, monomers other than the above describedcopolymer component can be copolymerized within the range that theeffects of the present invention are not lost, for example, about 0.5 to10% by mol.

Examples of such monomers are olefins such as ethylene, propylene,isobutylene, α-octene, α-dodecene, α-octadecene; unsaturated acids suchas acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleicanhydride, and itaconic acid or salts, mono- or di-alkyl esters thereof;nitriles such as acrylonitrile and methacrylonitrile; amides such asdiacetoneacrylamide, acrylamide and methacrylamide; olefin sulfonic acidsuch as ethylene sulfonic acid, allyl sulfonic acid, and methacrylsulfonic acid or salts thereof; alkyl vinyl ethers; dimethylallyl vinylketone, N-vinyl pyrrolidone, vinyl chloride, vinylidene chloride;polyoxyalkylene(meth)allyl ether such as polyoxyethylene(meth)allylether and polyoxypropylene(meth)ally ether;polyoxyalkylene(meth)acrylate such as polyoxyethylene(meth)acrylate andpolyoxypropylene(meth)acrylate; polyoxyalkylene(meth)acrylamide such aspolyoxyethylene(meth)acrylamide and polyoxypropylene(meth)acrylamide;polyoxyethylene (1-(meth)acrylamide-1,1-dimethylpropyl)ester,polyoxyethylene vinyl ether, polyoxypropylene vinyl ether,polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylenevinylamine and polyoxypropylene vinylamine.

Further, examples are cation group-containing monomers such asN-acrylamidomethyl trimethylammonium chloride, N-acrylamidoethyltrimethylammonium chloride, N-acrylamidopropyl trimethylammoniumchloride, 2-acryloxyethyl trimethylammonium chloride,2-methacryloxyethyl trimethylammonium chloride, 2-hydroxy-3-methacryloyloxypropyl trimethylammonium chloride, allyl trimethylammonium chloride,methallyl trimethylammonium chloride, 3-butene trimethylammoniumchloride, dimethyl diallyl ammonium chloride and diethyl diallylammonium chloride, and acetoacetyl group-containing monomers.

As a polymerization method of copolymerizing a vinyl ester monomer withthe compound shown in the formula (1) (further with other monomers), itis not particularly limited, and known methods such as bulkpolymerization, solution polymerization, suspension polymerization,dispersion polymerization or emulsion polymerization can be employed,but usually solution polymerization is conducted.

The method for charging the monomer components when copolymerizing isnot particularly limited and the components can be added all at once, inportions or continuously. A dropping polymerization is preferable, apolymerization according to the HANNA method is particularly preferablefrom the viewpoints of physical properties such that the compound shownin the formula (1) is uniformly distributed into a molecular chain ofpolyvinyl ester polymer, reactivity with crosslinking agents isimproved, and a melting point of polyvinyl alcohol is lowered.

The solvent used for copolymerization is usually lower alcohols such asmethanol, ethanol, isopropyl alcohol, propanol and butanol, and ketonessuch as acetone and methyl ethyl ketone. Methanol is suitably used froman industrial point of view.

An amount of the solvent that is used can be selected accordingly inview of the chain transfer constant of the solvent, depending on thedesired polymerization degree of the copolymer. For example, whenmethanol is the solvent, the amount is selected from the range of S(solvent)/M (vinyl ester monomer)=0.01 to 10 (weight ratio), preferably0.05 to 3 (weight ratio).

A polymerization catalyst is used in the copolymerization, and examplesof the polymerization catalyst are, for instance, known radicalpolymerization catalysts such as azobisisobutyronitrile, acetylperoxide, benzoyl peroxide, lauryl peroxide, and radical polymerizationcatalysts active at low temperatures such as azobisdimethylvaleronitrileand azobismethoxydimethylvaleronitrile.

The amount of the polymerization catalyst that is used depends on thetype of catalyst and cannot be categorically determined, but is selectedarbitrarily according to the polymerization rate. For example, in thecase that azobisisobutyronitrile or acetyl peroxide is used, the amountis preferably 0.01 to 0.2% by mol, particularly preferably 0.02 to 0.15%by mol, based on the vinyl ester monomer.

Also, the reaction temperature of the copolymerization reaction ispreferably selected from the range of 40° C. to the boiling pointdepending on the solvent that is used and the pressure.

In the present invention, a copolymerization ratio of the compound shownin the formula (1) is not particularly limited, and may be determined inaccordance with an introduction amount of 1,2-glycol bonds describedbelow.

Then, the obtained copolymer is hydrolyzed but the hydrolyzing iscarried out in a state in which the obtained copolymer is dissolved inalcohol or alcohol containing water, using alkali catalyst or acidcatalyst. Examples of the alcohol are methanol, ethanol, propanol andtert-butanol and methanol is preferably used in particular. Theconcentration of the copolymer in the alcohol is suitably selectedaccording to the viscosity of the system, but usually selected from arange of 10 to 60% by weight. Examples of the catalyst used for thehydrolyzing are alkali catalysts such as the hydroxides of alkali metaland alcoholates including sodium hydroxide, potassium hydroxide, sodiummethylate, sodium ethylate, potassium methylate and lithium methylate;and acid catalysts such as sulfuric acid, hydrochloric acid, nitricacid, methanesulfonic acid, zeolite and cation-exchange resin.

The amount of the hydrolyzing catalyst is suitably selected according tothe hydrolyzing method, the desired degree of hydrolyzing and the like,but when an alkali catalyst is used, the amount is suitably 0.1 to 30millimoles and preferably 2 to 17 millimoles, based on 1 mole of thetotal amount of vinyl ester monomer and the compound shown in theformula (1).

Also, a reaction temperature of the hydrolysis reaction is notparticularly limited, but preferably 10 to 60° C., more preferably 20 to50° C.

The polyvinyl alcohol of the present invention is prepared bysimultaneous conversion of an ester part of a vinyl ester monomer and anacyloxy part of the compound shown in the formula (1) into hydroxylgroups, it has a feature that byproduct such as dimethyl carbonate isnot generated, which is a drawback in the case of using vinyl ethylenecarbonate.

In the present invention, the average polymerization degree of thepolyvinyl alcohol (measured in accordance with JIS K6726) is 150 to4000, preferably 300 to 2600, and particularly preferably 500 to 2200.When the average polymerization degree is less than 150, mechanicalstrength tends to be lowered in the use for film application, when theaverage degree of polymerization exceeds 4000, it tends to be difficultto introduce many 1,2-glycol bonds.

Also, the hydrolysis degree of the polyvinyl alcohol is preferably atleast 60% by mol, more preferably at least 70% by mol, still morepreferably at least 80% by mol, and particularly preferably at least 90%by mol. When the hydrolysis degree is less than 60% by mol, watersolubility tends to be lowered.

Additionally, a hydrolysis degree in the present invention is expressedas a conversion rate (% by mol) of the total amount of the ester part ofthe vinyl ester monomer and the acyloxy part of the compound shown inthe formula (1) into hydroxyl groups (in the hydrolysis reaction, anacyloxy part of the compound shown in the formula (1) is almostcompletely hydrolyzed in a degree of hydrolysis of 70 to 80% by mol.

An upper limit of the hydrolysis degree comparatively varies accordingto applications. In the case of using for an adhesive for aqueous vinylurethane, a paper processing agent (sizing agent) or various kinds ofsilica binders for an ink receiving layer and a gloss layer in an inkjet paper, it is preferably less than 99.0% by mol. For the applicationof acid or alkali packaging materials of agricultural chemicals,detergents and the like, the hydrolysis degree is preferably at least99.0% by mol from the viewpoint of exhibiting a characteristic reactiveeffect that water solubility of a film hardly changes with time.

Additionally, the amount of 1,2-glycol bonds introduced in a polyvinylalcohol is not particularly limited, it is preferably 0.1 to 40% by mol,more preferably 0.5 to 25% by mol, and further preferably 1 to 20% bymol. When the introduction amount is less than 0.1% by mol, reactivitywith a crosslinking agent is low in the case of using the crosslinkingagent etc together, also, viscosity stability when formed to be anaqueous solution tends to be lowered, further, the coating property alsotends to be lowered in the case where the aqueous solution is used in ahigh-speed coating application. When the introduction amount exceeds 40%by mol, the polymerization degree tends to become too low.

Particularly, in the present invention, as described above, even in thecase where the amount of 1,2-glycol bonds is introduced as high as atleast 7% by mol, there is no problem caused in industrial practice, thepreparation thereof can be easily conducted, furthermore, a polyvinylalcohol with a high introduction amount decreases in crystallinity toresult in increasing in water solubility, also stability of an aqueoussolution of the polyvinyl alcohol is excellent, the aqueous solution ofthe polyvinyl alcohol is low foaming, and a film obtained from theaqueous polyvinyl alcohol is not lowered in water solubility even ifleft under an alkali atmosphere for a long period of time, therefore, itis useful for water soluble packing material applications such aspackage for alkali detergent. Also, on the other hand, 1,2-glycol bondhas a primary hydroxyl group, the introduction amount can be largelyincreased, so that adhesion strength can be significantly improved whenit is used in application of an aqueous vinyl urethane adhesive, it isuseful as adhesives for woodwork, particularly for softwood plywood.Also, it has a high interaction with silica such as colloidal silica andfumed silica, it is also suitable for a gloss layer for ink jet.

The polyvinyl alcohol of the present invention has a low melting pointeven having a high degree of hydrolysis of approximately 99% by mol,thus, when the polyvinyl alcohol of the present invention is blendedwith a compatiblizer (various kinds of acid anhydride modified olefinresin such as maleic anhydride, into olefin resin such as anethylene-vinyl acetate copolymer (content of vinyl acetate ofapproximately 1 to 40% by weight), melt blending is easily carried out.Also, it has usefulness such that, for example, by blending about 20% byweight of polyvinyl alcohol of the present invention with theethylene-vinyl acetate copolymer, a film for agriculture with the samewarmth retaining property as a vinyl chloride film can be obtained.

The polyvinyl alcohol having a 1,2-glycol bond in a side chain of thepresent invention has low crystallinity even with a high hydrolysisdegree, so that it has high velocity of dissolution into water, exhibitsvery excellent effect on standing stability of the aqueous solution,further, because a hydroxyl group is present as a primary alcohol, ithas also high reactivity with a crosslinking agent such as an isocyanatecompound, polyamide epichlorohydrin, glyoxal, melamine resin,methylolmelamine, methylolated bisphenol S, and dimethylolated urea. Asthe isocyante compound, isocyanate having at least two isocyanate groupsin a molecule is useful, examples are, for instance, tolylenediisocyanate (TDI), hydrogenated TDI, trimethylolpropane-TDI adduct(e.g. “Desmodur (registered trademark) L” available from Bayer AG),triphenylmethane triisocyanate, methylenebisdiphenyl isocyanate (MDI),hydrogenated MDI, polymerized MDI, hexamethylene diisocyanatae, xylylenediisocyanate, 4,4-dicyclohexylmethane diisocyanate and isophoronediisocyanate. In addition, an other example is a prepolymer having anisocyante group at an end group previously polymerized with excesspolyisocyanate in polyol. A composition ratio of the isocyanate compoundis preferably 0.1 to 2 of mole ratio of an isocyanate group to ahydroxyl group (NCO/OH). Also, it has a favorable coating propertywithout increasing viscosity under high shear at high speed coating.Furthermore, it has high reactivity with aldehydes in butyralizing andacetalizing, a butyral resin with high flexibility can be obtained.

The polyvinyl alcohol of the present invention can be used in variouskinds of applications, a part of the applications are described above,and specific examples are described in the following.

(1) Adhesive Application

Adhesives tackifiers and re-wetting agents for wood, paper, aluminumfoil and plastic, binder for non-woven fabrics, various kinds ofbuilding material binders for a plaster board and a fiber board, variouskinds of binders for powder granulation, additives for cement andmortar, hot melt type adhesives, pressure sensitive adhesives, andfixing agents of anionic paint.

(2) Molded Article Application

Fibers, films (particularly easy-water-soluble films for wrapping goodssuch as agriculture chemicals, detergents, clothing for laundry,additives for civil engineering, bactericides, dyes and pigments: thehydrolysis degree of the polyvinyl alcohol is preferably at least 65% bymol), raw films for polarizing films (the amount of 1,2-glycol bond ispreferably 0.2 to 2% by mol and the polymerization degree is preferablyat least 2000), sheets, pipes, tubes, leakage protecting films,temporary films, chemical laces and water soluble fibers.

(3) Coating Agent Application

Clear coating agents for paper, pigment coating agents for paper, sizingagents for paper, sizing agents for fiber products, adhesive pastes forwrap yarn, fiber processing agents, leather finishing agents, paints,defogging agents, metal corrosion proofing agents, lubricants for zincplating, anti-static agents, conducting agents and temporary paints.

(4) Emulsifier Application

Emulsifiers for emulsion polymerization of ethylenically unsaturatedcompounds, butadiene compounds and various kinds of acrylic monomers;and post emulsifiers for hydrophobic resins such as polyolefin,polyester resin and the like, epoxy resin, paraffin and bitumen.

(5) Suspending Agent Application

Pigment dispersion stabilizers for paints, black writing fluid, aqueouscolor ink and adhesives; and dispersion stabilizers for suspensionpolymerization of various kinds of vinyl compounds such as vinylchloride, vinylidene chloride, styrene, (meth)acrylate and vinylacetate.

(6) Blending Agent for Hydrophobic Resin Application

Antistatic agents and hydrophilicity imparting agents for hydrophobicresin; and additives for molded articles such as conjugate fibers, films(especially, films applied for agriculture can be provided with warmthretaining property).

(7) Thickener Application

Thickeners for various kinds of aqueous solutions and emulsions.

(8) Coagulant Application

Coagulants for aqueous suspension and dissolved matter, and filteringagents for pulp and slurry.

(9) Soil Improving Agent Application

(10) Photosensitizing Agent, Electro-Sensitive Application andPhotosensitive Resin

(11) Ion-Exchange Resin, Ion-Exchange Membrane, Chelate Exchange Resin,and Others

Among the above descriptions, usefulness in applications of (1) to (5)is particularly expected.

Additionally, in developing various applications, it is preferable toadd a plasticizer according to necessity, and examples of theplasticizer are polyhydric alcohol of tervalent to hexavalent (glycerin,trimethylolpropane, diglycerin, pentaerythritol, xylose, arabinose,ribulose, sorbitol and the like), various alkylene oxides (ethyleneoxide, propylene oxide, mixed adduct of ethylene oxide and propyleneoxide, and the like).

EXAMPLES

The present invention is specifically explained below with reference toExamples, however the present invention is not limited to the followingexamples.

Additionally, “part” and “%” represent weight standards unless indicatedotherwise.

Example 1

Into a reactor equipped with a reflux condenser, a dropping funnel and astirrer, 1300 g of vinyl acetate, 650 g of methanol and 78.1 g (3% bymol based on the charged vinyl acetate) of 3,4-diacetoxy-1-butene werecharged, 0.06% by mol (based on the charged vinyl acetate) ofazobisisobutyronitrile was added thereto, and polymerization was carriedout increasing a temperature under nitrogen flow while stirring.

Then, at a point that a polymerization ratio of vinyl acetate reached87.5%, 50 ppm (based on the charged vinyl acetate) of m-dinitrobenzenewas charged thereto as a polymerization inhibitor to completepolymerization. Subsequently, by a method of blowing methanol vapor,unreacted vinyl acetate monomers were removed outside the system toobtain the methanol solution of the copolymer.

Then, the solution was diluted with methanol to adjust a concentrationat 40%, charged into a kneader, while maintaining a temperature of thesolution at 40° C., a 2% methanol solution of sodium hydroxide was addedfor its ratio to be 8% by mmol based on the total amount of vinylacetate and 3,4-diacetoxy-1-butene to conduct hydrolysis. The hydrolyzedproduct was separated by filteration at the point of time when thehydrolyzed product was precipitated to form particles as hydrolysisproceeded, sufficiently washed with methanol, dried in a hot air dryerto obtain the polyvinyl alcohol.

In the above preparation of the polyvinyl alcohol, waste liquid aftercompletion of hydrolysis was examined for presence of byproduct usingGC-MS (“597N GC/MSD” system manufactured by Agilent Technologies, Inc.)in the following conditions.

(Column Conditions)

-   Column: HP-WAX (crosslinked polyethyleneglycol) capillary column-   Column temperature: fixed at 40° C. for 5 min, raising a temperature    at 10° C./min, allowed to stand at 240° C. for 10 min-   Inlet temperature: 240° C.-   Carrier gas: He-   Column flow rate: 1.0 ml/min    (MS Part Conditions)-   Apparatus used: “5973MSD” system manufactured by Agilent    Technologies, Inc.-   Mass range: 10 to 600-   Threshold: 20-   Scan/sec.: 2.54

As a result, dimethyl carbonate was not detected. Also, any salt otherthan sodium acetate was not detected.

The hydrolysis degree of the obtained polyvinyl alcohol (I) was analyzedas an amount of alkali consumption required for hydrolysis of residualvinyl acetate and residual 3,4-diacetoxy-1-butene to find 99.5% by mol,the average polymerization degree was analyzed in accordance with JIS K6726 to find 870. Also, the viscosity of the polyvinyl alcohol in a 4%aqueous solution was measured by a Hoppler viscometer to find 8.6 mPa·s(20° C.), the introduction amount of 1,2-glycol bonds was measured by¹H-NMR (internal standard substance: tetramethylsilane, solvent:d6-DMSO) and calculated to be 3.1% by mol. Additionally, “AVANCE DPX400”manufactured by Bruker Japan Co., Ltd. was used for NMR measurement.

[¹H-NMR] (see FIG. 1)

-   1.2 to 1.5 ppm: Methylene proton-   1.8 ppm: Methine proton (due to denaturalization)-   3.5 ppm: Methylene proton of primary methylol-   3.82 to 3.84 ppm: Methine proton-   4.13 to 4.6 ppm: Hydroxyl group-   4.25 ppm: Hydroxyl group of diol

Also, polyvinyl alcohol (II) [partly hydrolyzed product (the hydrolysisdegree of 84.2% by mol)] was obtained by sampling in a process ofhydrolysis, ¹H-NMR chart of the polyvinyl alcohol (II) (solvent:d6-DMSO) was as follows.

[¹H-NMR] (see FIG. 2)

-   1.36 to 1.8 ppm: Methylene proton-   1.93 to 1.95 ppm: Methyl proton-   3.5 ppm: Methylene proton of primary methylol-   3.8 ppm: Methine proton-   4.15 to 4.57 ppm: Hydroxyl group-   4.3 ppm: Hydroxyl group of diol-   4.7 to 5.2 ppm: Methine proton

The obtained polyvinyl alcohols (I) and (II) were evaluated as follows.

(Solubility)

The obtained polyvinyl alcohol was dried at 150° C. for 3 hours, after a10% aqueous solution was prepared, the aqueous solution was filteredthrough a 400-mesh metal net, the residue of the filtration was measuredand evaluated as follows. The evaluation results are shown in Table 1.

-   ◯: residue of filtration is less than 0.005%-   Δ: residue of filtration is at least 0.005% to not more than 0.01%-   x: residue of filtration is more than 0.01%

Example 2

Into a reactor equipped with a reflux condenser, a dropping funnel and astirrer, 1300 g of vinyl acetate, 190 g of methanol and 60.5 g (2.28% bymol based on the charged vinyl acetate) of 3,4-diacetoxy-1-butene (B)were charged, 0.06% by mol (based on the charged vinyl acetate) ofazobisisobutyronitrile was added thereto. Temperature was raised undernitrogen flow while stirring and polymerization was started at 67° C.,simultaneously, 116 ml of a 5.4% methanol solution of3,4-diacetoxy-1-butene was uniformly added dropwise up to apolymerization ratio of 85.3%.

The polymerization was terminated at the point that a polymerizationratio of vinyl acetate reached 85.3%, subsequently, by a method ofblowing methanol vapor, unreacted vinyl acetate monomers were removedoutside the system to obtain the methanol solution of the copolymer.

Then, the solution was diluted with methanol to adjust a concentrationat 40%, charged into a kneader, while maintaining a temperature of thesolution at 40° C., a 2% methanol solution of sodium hydroxide was addedfor its ratio to be 9% by mmol based on the total amount of vinylacetate and 3,4-diacetoxy-1-butene to conduct hydrolysis. The hydrolyzedproduct was separated by filteration at the point of time when thehydrolyzed product was precipitated to form particles as hydrolysisproceeded, sufficiently washed with methanol, dried in a hot air dryerto obtain the polyvinyl alcohol.

In the above preparation of the polyvinyl alcohol, waste liquid aftercompletion of the hydrolysis was examined in the same method as inExample 1 to detect no dimethyl carbonate.

The hydrolysis degree of the obtained polyvinyl alcohol (I) was analyzedas an amount of alkali consumption required for hydrolysis of residualvinyl acetate and 3,4-diacetoxy-1-butene to find 99.6% by mol, theaverage degree of polymerization was analyzed in accordance with JIS K6726 to find 1320. Also, the viscosity of the polyvinyl alcohol in a 4%aqueous solution was measured by a Hoppler viscometer to find 18.7 mPa·s(20° C.), the introduction amount of 1,2-glycol bonds was measured by¹H-NMR (internal standard substance: tetramethylsilane, solvent:d6-DMSO) and calculated to be 3.2% by mol. Also, the polyvinyl alcohol(II) [partly hydrolyzed product (hydrolysis degree of 95.0% by mol)] wasobtained by sampling in a process of hydrolysis. The obtained polyvinylalcohols (I) and (II) were evaluated in the same manner as in Example 1.The evaluation results are shown in Table 1.

Example 3

Into a reactor equipped with a reflux condenser, a dropping funnel and astirrer, 1000 g of vinyl acetate (A), 50 g of methanol and3,4-diacetoxy-1-butene (6% by mol based on the charged vinyl acetate)were charged, 0.03% by mol (based on the charged vinyl acetate) ofazobisisobutyronitrile was added thereto, and polymerization was carriedout increasing a temperature under nitrogen flow while stirring. At apoint that a polymerization ratio of vinyl acetate reached 72%, apolymerization inhibitor was charged thereto to terminatepolymerization. Subsequently, by a method of blowing methanol vapor,unreacted vinyl acetate monomers were removed outside the system toobtain the methanol solution of the copolymer.

Then, the solution was diluted with methanol to adjust a concentrationat 40%, charged into a kneader, while maintaining a temperature of thesolution at 40° C., a 2% methanol solution of sodium hydroxide was addedfor its ratio to be 8% by mmol based on the total amount of vinylacetate and 3,4-diacetoxy-1-butene to conduct hydrolysis. As thehydrolysis proceeded, the hydrolyzed product was separated out andbecame particles at last. The obtained polyvinyl alcohol was collectedby filtration, sufficiently washed with methanol, and dried in a hot airdryer to obtain the polyvinyl alcohol.

The hydrolysis degree of the obtained polyvinyl alcohol (I) was analyzedas an amount of alkali consumption required for hydrolysis of residualvinyl acetate and 3,4-diacetoxy-1-butene to find 99.5% by mol, theaverage polymerization degree was analyzed in accordance with JIS K 6726to find 1450. Also, the viscosity of the polyvinyl alcohol in a 4%aqueous solution was measured by a Hoppler viscometer to find 18.6 mPa·s(20° C.), an introduction amount of 1,2-glycol bonds was measured by¹H-NMR (internal standard substance: tetramethylsilane, solvent:d6-DMSO; see FIG. 3) and calculated to be 6.2% by mol. Also, thepolyvinyl alcohol (II) [partly hydrolyzed product (hydrolysis degree of87.8% by mol)] was obtained by sampling in a process of hydrolysis. Theobtained polyvinyl alcohols (I) and (II) were evaluated in the samemanner as in Example 1. The evaluation results are shown in Table 1.

Example 4

Into a reactor equipped with a reflux condenser, a dropping funnel and astirrer, 1000 g of vinyl acetate, 50 g of methanol and3,4-diacetoxy-1-butene (15% by mol based on the charged vinyl acetate)were charged, 0.06% by mol (based on the charged vinyl acetate) ofazobisisobutyronitrile was added thereto, and polymerization was carriedout increasing a temperature under nitrogen flow while stirring. At apoint that a polymerization ratio of vinyl acetate reached 70%, apolymerization inhibitor was charged to terminate the polymerization.Subsequently, by a method of blowing methanol vapor, unreacted vinylacetate monomers were removed outside the system to obtain a methanolsolution of the copolymer.

Then, the solution was diluted with methanol to adjust a concentrationat 40%, charged into a kneader, while maintaining a temperature of thesolution at 40° C., a 2% methanol solution of sodium hydroxide was addedfor its ratio to be 11% by mmol based on the total amount of vinylacetate and 3,4-diacetoxy-1-butene to conduct hydrolysis. As thehydrolysis proceeded, the hydrolyzed product was separated out andbecame particles at last. The obtained polyvinyl alcohol was collectedby filtration, sufficiently washed with methanol, and dried in a hot airdryer to obtain a polyvinyl alcohol.

The hydrolysis degree of the obtained polyvinyl alcohol (I) was analyzedas an amount of alkali consumption required for hydrolysis of residualvinyl acetate and 3,4-diacetoxy-1-butene to find 99.2% by mol, theaverage polymerization degree was analyzed in accordance with JIS K 6726to find 900. Also, the viscosity of the polyvinyl alcohol in a 4%aqueous solution was measured by a Hoppler viscometer to find 9.5 mPa·s(20° C.), an introduction amount of 1,2-glycol bonds was measured by¹H-NMR (internal standard substance: tetramethylsilane, solvent:d6-DMSO) and calculated to be 14.9% by mol. Also, the polyvinyl alcohol(II) [partly hydrolyzed product (the degree of hydrolysis of 87.8% bymol)] was obtained by sampling in a process of hydrolysis. The obtainedpolyvinyl alcohols (I) and (II) were evaluated in the same manner as inExample 1. The evaluation results are shown in Table 1.

Comparative Example 1

A polyvinyl alcohol having a 1,2-glycol bond in a side chain wasobtained and evaluated in the same manner as in Example 1 except thatvinyl ethylene carbonate shown in the following formula (2) was usedinstead of 3,4-diacetoxy-1-butene.

Additionally, waste liquid after completion of hydrolysis was examinedin the same method as in Example 1 to detect a large amount of dimethylcarbonate, it was necessary to have a hydrolysis process of dimethylcarbonate in the solvent recovery process.

The hydrolysis degree of the obtained polyvinyl alcohol (I) was analyzedas an amount of alkali consumption required for hydrolysis of residualvinyl acetate unit to find 99.5% by mol, an average polymerizationdegree was analyzed in accordance with JIS K 6726 to find 1220. Also, aviscosity of the polyvinyl alcohol in a 4% aqueous solution was measuredby a Hoppler viscometer to find 15.1 mPa·s (20° C.), an introductionamount of 1,2-glycol bonds was measured by ¹H-NMR (internal standardsubstance: tetramethylsilane, solvent: d6-DMSO) and calculated to be2.8% by mol. Also, the polyvinyl alcohol (II) [partly hydrolyzed product(the hydrolysis degree of 81.9% by mol)] was obtained by sampling in aprocess of hydrolysis. The obtained polyvinyl alcohols (I) and (II) wereevaluated in the same manner as in Example 1. The evaluation results areshown in Table 1.

Comparative Example 2

Preparation of a polyvinyl alcohol having a 1,2-glycol bond in a sidechain of 15% by mol was tried in the same manner as in ComparativeExample 1 except for satisfying a relation of S/M=0.05 (S: methanol (50g), M: vinyl acetate (1000 g), polymerization ratio of 70%) and charging205 g (15.5% by mol) of vinyl ethylene carbonate.

Though a copolymer was obtained, but, when residual unreacted vinylacetate was removed after completion of polymerization while chargingmethanol, there arose a problem that the polymer was precipitated inmethanol.

Also, precipitation of the copolymer into a methanol solvent wasobserved in hydrolysis of the copolymer, inhomogeneous hydrolysis wasnot avoided. Also, waste liquid after completion of the hydrolysis wasexamined in the same method as in Example 1 to detect a large amount ofdimethyl carbonate, it was necessary to have a hydrolysis process ofdimethyl carbonate in the solvent recovery process.

A hydrolysis degree of the obtained polyvinyl alcohol (I) was analyzedas an amount of alkali consumption required for hydrolysis of residualvinyl acetate unit to find 99.5% by mol, an average polymerizationdegree was analyzed in accordance with JIS K 6726 to find 720. Also, theviscosity of the polyvinyl alcohol in a 4% aqueous solution was measuredby a Hoppler viscometer to find 7.5 mPa·s (20° C.), an introductionamount of 1,2-glycol bonds was measured by ¹H-NMR (internal standardsubstance: tetramethylsilane, solvent: d6-DMSO) and calculated to be 15%by mol. Also, the polyvinyl alcohol (II) [partly hydrolyzed product(hydrolysis degree of 85.1% by mol)] was obtained by sampling in aprocess of hydrolysis. The obtained polyvinyl alcohols (I) and (II) wereevaluated in the same manner as in Example 1. The evaluation results areshown in Table 1.

TABLE 1 Solubility Polyvinyl alcohol (I) (II) Ex. 1 ∘ ∘ Ex. 2 ∘ ∘ Ex. 3∘ ∘ Ex. 4 ∘ ∘ Com. Ex. 1 Δ x Com. Ex. 2 Δ x

Example 5

Using the polyvinyl alcohols (I) and (II) obtained in Example 1, atwo-liquid type adhesive was prepared in the following manner.

[Preparation of Two-Liquid Type Adhesive]

The following base resin (aqueous emulsion with solid content of 43.5%)and a curing agent (multivalent isocyanate compound) were prepared.

(Base Resin)

-   15% aqueous solution of polyvinyl alcohol (I) or (II): 40 parts-   Emulsion of styrene-butadiene copolymer with solid content of 50%    (“DL612” available from Asahi Kasei Corporation): 35 parts-   Calcium carbonate: 20 parts-   Water: 5 parts    (Curing Agent)-   MDI (content of NCO group of 6.71×10⁻³ mol/g): 9.72 parts

Then, the two-liquid type adhesive prepared above was mixed withstirring, and the following evaluations were carried out. The evaluationresults are shown in Table 2.

(Adhesion Strength in Normal Conditions)

On one surface of two pieces of birch board having straight grain (10mm×25 mm×30 mm), the above adhesive was applied so as to be 100±10 g/m²,both applied surfaces were stuck and pressed with a pressure of 8 kg/cm²for 12 hours, then adhesion strength was measured in accordance with JISK 6852.

(Initial Adhesion Strength)

Both surfaces of birch wood were stuck in the same manner as in theabove description (adhesion strength in normal conditions), and pressedwith a pressure of 8 kg/cm² for 5 minutes or 10 minutes, then adhesionstrength was measured in accordance with JIS K 6852.

(Endurance Adhesion Strength)

An adhesion sample was prepared in the same manner as in the abovedescription (adhesion strength in normal conditions), after aging at 25°C. for 6 days, it was immersed in boiling water for 5 hours, dried inair at 60° C. for 24 hours, further, immersed in boiling water for 4hours, then, was left to stand till being cooled in water of a roomtemperature, taken out from water, and immediately after that, adhesionstrength (still in wet) was measured in accordance with JIS K 6852.

Examples 6 to 8

Using the polyvinyl alcohols (I) and (II) obtained in Example 2 (Example6) to Example 4 (Example 8), the evaluations were carried out in thesame manner as in Example 5. The evaluation results are shown in Table2.

Comparative Example 3

Two kinds of polyvinyl alcohols were obtained in the same manner as inExample 1 except that 3,4-diacetoxy-1-butene was not used, only vinylacetate was polymerized (S/M=0.5:S:methanol (500 g), M: vinyl acetate(1000 g)) and hydrolyzed.

The hydrolysis degree of the obtained polyvinyl alcohols were analyzedas amounts of alkali consumption required for hydrolysis of residualvinyl acetate unit to find 99.1% by mol (the polyvinyl alcohol (I)) and88.2% by mol (the polyvinyl alcohol (II)), an average polymerizationdegree was analyzed in accordance with JIS K 6726 to find 1200.

Using the obtained polyvinyl alcohols, the evaluations were carried outin the same manner as in Example 5. The evaluation results are shown inTable 2.

TABLE 2 Adhesion strength Endurance in normal Initial adhesion strengthadhesion conditions after 5 min. after 10 min. strength Ex. 1 194/21041/51 53/58 119/123 Ex. 2 215/222 50/53 63/65 127/131 Ex. 3 245/27052/62 63/72 137/141 Ex. 4 295/310 83/91  96/101 175/210 Com. Ex. 3130/180 21/27 29/36 51/54

Example 9

Using the polyvinyl alcohol (I) obtained in Example 1, after a film wasprepared in the following manner, the film was evaluated for cold watersolubility, alkali resistance and chemical resistance in the followingmanner. The evaluation results are shown in Table 3.

(Preparation of Film)

A 15% aqueous solution of the polyvinyl alcohol (I) was prepared, 15parts of glycerin was added based on 100 parts of the polyvinyl alcohol(I), and flow-cast on a heated roll of 70° C. to obtain a film having athickness of 50 μm.

(Cold Water Solubility)

The above film (3 cm×3 cm) was immersed in 1000 ml of water at 10° C.,and a time till the film was completely dissolved while stirring wasmeasured.

(Alkali Resistance)

Sodium carbonate was packed with a 10 cm×15 cm bag prepared by heatsealing the above film, left to stand in the condition of 40° C.×85 RH %for half a year, then, a piece of 3 cm×3 cm film was sampled from thebag, immersed in 1000 ml of water at 15° C., and a time till the filmwas completely dissolved while stirring was measured.

(Chemical Resistance)

It was evaluated in the same manner as the above description (alkaliresistance) except that trichloroisocyanuric acid was used instead ofsodium carbonate.

Examples 10 to 12 and Comparative Example 4

Using the polyvinyl alcohol (I) obtained in Example 2 (Example 10) toExample 4 (Example 12) and Comparative Example 3 (Comparative Example4), the evaluations were conducted in the same manner as in Example 9.The evaluation results were shown in Table 3.

Additionally, in Comparative Example 4, a film only swelled and did notdissolve in any evaluation.

TABLE 3 Cold water Alkali resistance Chemical solubility (sec.) (sec.)resistance (sec.) Ex. 9 30 39 35 Ex. 10 27 31 33 Ex. 11 20 21 24 Ex. 1212 16 18 Com. Ex. 4 swelling only swelling only swelling only

INDUSTRIAL APPLICABILITY

The polyvinyl alcohol of the present invention having a 1,2-glycol bondin a side chain is obtained by copolymerizing a compound shown in theformula (1) with a vinyl ester monomer, so that there is no generationof dimethyl carbonate in the preparation thereof, no need of aneliminating process of dimethyl carbonate in the recovering process ofwaste liquid after hydrolysis. Also, even when an introduction amount of1,2-glycol bonds is increased, there is no deterioration of solubilityin a hydrolyzing solution (methanol) of a copolymer (paste) beforehydrolysis, thus, it can be commercially produced in very useful method,further, it has a feature that the obtained polyvinyl alcohol(particularly partly hydrolyzed product) does not generatewater-insoluble part even in experiencing thermal history, it is usefulin workability and product quality in various applications ofconventional polyvinyl alcohol, particularly useful in the applicationsrelating to adhesives, molded articles, coating agents, emulsifiers andsuspending agents, in particular, it is useful for water solublepackaging material such as alkali detergent package or for adhesiveapplication of woodwork adhesive, above all, soft wood plywood.

1. An aqueous polyvinyl alcohol having a 1,2-glycol bond in a side chainobtained by hydrolyzing a copolymer of vinyl acetate and3,4-diacetoxy-1-butene, wherein the hydrolysis degree of the polyvinylalcohol is at least 60% by mol and less than or equal to 99.6% by mol,wherein the ratio of structural units derived from3,4-diacetoxy-1-butene to structural units derived from vinyl acetate isfrom 0.1:100 to 20:100.
 2. The aqueous polyvinyl alcohol of claim 1,wherein the hydrolysis degree is at least 99.0% by mol.
 3. The aqueouspolyvinyl alcohol of claim 1, wherein the hydrolysis degree is less than99.0% by mol.
 4. A process for preparing an aqueous polyvinyl alcoholhaving a 1,2-glycol bond in a side chain, wherein a copolymer of vinylacetate and 3,4-diacetoxy-1-butene is hydrolyzed such that thehydrolysis degree of the polyvinyl alcohol is at least 60% by mol,wherein the polyvinyl alcohol either does not contain structural unitsderived from ethylene, or contains from about 0.5 to 10% by mol ofstructural units derived from ethylene.
 5. The process for preparing anaqueous polyvinyl alcohol of claim 4, wherein the hydrolysis degree isat least 99.0% by mol.
 6. The process for preparing an aqueous polyvinylalcohol of claim 4, wherein the hydrolysis degree is less than 99.0% bymol.
 7. The process for preparing an aqueous polyvinyl alcohol of claim4, wherein the ratio of structural units derived from3,4-diacetoxy-1-butene to structural units derived from vinyl acetate isfrom 0.1:100 to 20:100.